The present invention relates to a dynamic image transmission apparatus capable of transmitting dynamic image signals from a plurality of dynamic image signal sources to a plurality of dynamic image output apparatuses and, for example, to a dynamic image transmission apparatus that can be used in a dynamic image network for a TV meeting.
The present invention also relates to an image transmission apparatus for transmitting a plurality of dynamic image information signals through a multi-channel transmission path.
Furthermore, the present invention relates to an image transmission apparatus for encoding one-dimensional data such as voice data or two-dimensional data such as image data, and outputting decoded data.
A dynamic image transmission apparatus of this type is arranged as shown in, e.g., FIG. 34.
In FIG. 34, reference numerals 101a and 101b denote video cameras as dynamic image signal sources; and 102a to 102d, modulators each having a function of modulating a dynamic image signal output from the video camera 101a (101b) or a VTR 103a (103b) at a desired frequency, and outputting the modulated signal onto a coaxial cable 110. Reference numerals 103a and 103b denote VTRs; and 105a to 105c, demodulators each having a function of selectively demodulating a desired one of a plurality of dynamic image signals modulated by the modulators 102a to 102d, and output onto the coaxial cable 110. The modulators 102a to 102d, the coaxial cable 110, and the demodulators 105a to 105c form a dynamic image signal transmission channel. In this case, a multi-channel transmission path is constituted since a plurality of modulators and demodulators are used.
Reference numerals 106a to 106c denote output devices such as displays, video printers, and the like. The output devices 106a to 106c output dynamic image signals demodulated by the demodulators 105a to 105c.
The modulation frequencies used in the modulators 102a to 102d are controlled to utilize frequencies which are not used for transmission on the coaxial cable 110 at the beginning of transmission of dynamic image signals from the dynamic image signal sources.
As a second prior art, a dynamic image transmission apparatus comprises an arrangement shown in, e.g., FIG. 35 so as to synthesize dynamic images of a plurality of attendants, and to display synthesized dynamic images on each terminal.
More specifically, in FIG. 35, reference numerals 151a to 151c denote terminals A to C as motion picture signal sources; 155a and 155b, terminals D and E as dynamic image output devices; and 160, a coaxial cable as a transmission path.
In the terminals A to C (151a to 151c), reference numerals 152a to 152c denote image input devices A to C; and 153a to 153c, size converters A to C each having a function of converting a dynamic image of, e.g., the face of an attendant input at a corresponding one of the image input devices A to C (152a to 152c) into a desired size, and a function of modulating the input dynamic image signal at a desired frequency, and outputting the modulated signal onto the coaxial cable 160. The dynamic image signals which are converted into a desired size, and modulated by the size converters A to C (153a to 153c) are output onto the coaxial cable 160.
In the terminals D and E (155a and 155b), reference numerals 156a and 156b denote image synthesizers D and E for demodulating the modulated dynamic image signals from the coaxial cable 160, and synthesizing the three demodulated dynamic images from the terminals A to C (151a to 151c); and 157a and 157b, image output devices D and E such as displays.
FIG. 36 shows an example of dynamic images synthesized by the image synthesizers D and E (156a and 156b). More specifically, the image output devices D and E (157a and 157b) display the synthesized dynamic images, as shown in FIG. 36.
As a third prior art, an apparatus comprising an arrangement shown in, e.g., FIG. 37, is known.
In FIG. 37, reference numerals 171a to 171c denote image input devices F to H each having a function of receiving a dynamic image signal of, e.g., the face of an attendant, modulating the dynamic image signal at a desired frequency, and outputting the modulated signal onto a coaxial cable 180; and 172a and 172b, terminals F and G. The terminals F and G (172a and 172b) respectively comprise size converters F and G (173a and 173b) for demodulating the modulated dynamic image signals from the coaxial cable 180, and converting the demodulated dynamic image signals into a desired size, synthesizers F and G (174a and 174b) for synthesizing the dynamic image signals received from the image input devices and output from the size converters F and G (173a and 173b), as shown in, e.g., FIG. 36, and image output devices F and G (175a and 175b) for outputting the dynamic images synthesized by the synthesizers F and G (174a and 174b).
However, in the above-mentioned prior arts, since one channel having a predetermined transmission capacity is assigned to transmission of one dynamic image, when an image having a small information amount such a frame having a small number of high-frequency components of a dynamic image to be transmitted is transmitted, the transmission capacity of the transmission channel is partially wasted, resulting in poor utilization efficiency of the transmission path of the entire network.
In particular, in the second prior art, for example, when it is attempted at the terminal D 155a to display only an image A from the terminal A 151a in a large scale, the operation of the size converter A 153a of the terminal 151a must be switched. However, since the terminals D 155a and E 155b share the received dynamic image signals, the image A is also displayed in a large scale on the terminal E 155b. In this manner, in the second prior art, it is impossible to change the output image size according to a request from a reception-side terminal without influencing an output image on another reception terminal.
In the third prior art, since the size converters F and G (173a and 173b) are arranged on the reception-side terminals F and G (172a and 172b), each terminal can output an image in a desired scale without influencing an output image on another reception terminal. However, since a transmission-side terminal cannot detect the size of a dynamic image signal requested by the reception-side terminal, even when the reception-side terminal requests only a reduced image signal, the transmission-side terminal must output an image onto the transmission path without reducing the image, i.e., without compressing the transmission band. For this reason, the frequency band of the transmission path is wastefully used.
As a conventional transmission system for transmitting dynamic image information in multi-channels, for example, the following system is known. In this system, a multi-channel transmission path is constituted by using a coaxial cable, and a plurality of modulators and demodulators, and a plurality of dynamic image information signals are transmitted.
However, in a transmission system of this type, when all the transmission channels of the multi-channel transmission path are busy, a transmission request of newly generated dynamic image information must wait until one of the transmission channels is ready, resulting in poor response to a transmission request.
As a method of solving this problem, the rights of use of transmission channels are sequentially changed in a predetermined time unit, thereby realizing transmission of dynamic image information signals numbering more than the number of transmission channels of the multi-channel transmission path. In this case, every time the right of use of the transmission channel is lost, dynamic image information is undesirably disconnected.
Furthermore, in the conventional transmission system, the transmission capacity per transmission channel is uniformly and permanently assigned. For this reason, when dynamic image information having a small information amount to be transmitted is transmitted, e.g., when a reception-side terminal requests to display an image in a reduced scale, the transmission capacity is not fully utilized, and is partially wasted, resulting in poor utilization efficiency of the transmission path of the entire network.
As still another image transmission apparatus, for example, an apparatus, which encodes an image by a differential encoding transmission method, and transmits the encoded image, as shown in FIG. 38, is known. In FIG. 38, an input dynamic image signal 871 to be transmitted is input to an A/D converter 872 for converting the dynamic image signal into a digital signal, and a system clock generator 873 for extracting a sync signal from the input dynamic image signal, and generating various system clocks to be used in the system. A delay device 874 delays the A/D-converted image signal by one system clock period (T.sub.0).
A subtracter 875 calculates the difference between image signals of adjacent pixels sampled at an interval of one system clock period. A modulator 876 modulates the output from the subtracter 875 in correspondence with the format of the transmission path, and outputs the modulated data.
In still another conventional image transmission apparatus, as shown in FIG. 39, an input dynamic image signal 881 is transmitted through a plurality of transmission channels and a plurality of differential encoders 1 to n (883 to 885) using a plurality of interleaved system clocks from a system clock generator 882, thereby prolonging the system clock period.
However, in the conventional image transmission apparatus shown in FIG. 38, the period of system clocks obtained from the system clock generator is equal to the sampling period of adjacent pixels to be sampled, and is normally as fast as 100 nsec or less. For this reason, the A/D converter, the delay device, the subtracter, and the modulator, which operate based on the system clocks, are required to perform high-speed operations. As a result, it is difficult to manufacture and adjust the apparatus, resulting in an increase in cost.
In the prior art shown in FIG. 39, an image signal transmitted through each differential encoder has a low image redundancy (self correlation) since it is constituted by non-adjacent pixels of an input dynamic image signal. For this reason, the number of bits upon quantization must be increased, thus deteriorating encoding efficiency.
In still another conventional dynamic image transmission apparatus, for example, as shown in FIG. 40, video signals output from a plurality of video cameras 981 and VTRs 982 are modulated at desired frequencies by modulators 983, and the modulated signals are sent onto a coaxial cable 984. The video signals from the coaxial cable 984 are received by demodulators 985. The video signals modulated by the modulators 983 are demodulated by the demodulators 985.
A plurality of demodulated input video signals are input to and synthesized by a synthesizer 986, and the synthesized video signals are displayed on a monitor television (TV) 987. The video signals output from the synthesizer 986 can be recorded by a video printer 988.
However, in this conventional dynamic image transmission apparatus, when a plurality of video signals from the video cameras 981 and VTRs 982 as dynamic image sources are synthesized, and are displayed on the monitor TV 987, since the modulators 983 individually assign modulation frequency bands corresponding to transmission channels to the plurality of video signals, the number of transmission channels is inevitably increased as compared to a case wherein a video signal from a single dynamic image source is displayed on the monitor TV 987.
When a plurality of display requests for displaying a plurality of video signals on the monitor TV 987 connected to the apparatus are simultaneously issued, it is often impossible to meet such display requests due to the limitation on the transmission capacity of the coaxial cable 984.
Conventionally, most apparatuses of this type convert input data into data in a frequency region using an orthogonal transform method such as a DCT (Discrete Cosine Transform) method, and compress the data amount by using control of, e.g., quantization characteristics of a quantizer such as nonlinear quantization, assignment of the number of quantization bits, and the like in correspondence with the statistical nature of input data, a run length method for totalizing converted zero data, and the like.
However, in the orthogonal transform method using the DCT method, N.sup.2 multiplications using a cosine function as a coefficient must be performed for N input data, as shown in the following equation: ##EQU1##
Since the orthogonal transform precision depends on the bit length of the coefficient of the cosine function, the bit length of the coefficient of the cosine function is set to be large. For this reason, it takes much time for a multiplication between the coefficient of the cosine function and input data, and the scale of a processing circuit is also increased. Therefore, an encoding/decoding device using such a DCT method has a low processing speed, and cannot be rendered compact.